This disclosure relates to a method for shifting from a first gear to a second gear in a dual clutch transmission during vehicle acceleration or retardation, which includes disengaging a tooth clutch of an inactive gear in the dual clutch transmission having an electric motor drivingly connected to a transmission shaft. The disclosure also relates to dual clutch transmission with an electric motor drivingly connected to a transmission shaft for a vehicle.
The method and dual clutch transmission may be used for a transmission in a utility vehicle, such as a truck or bus, or a construction vehicle such as wheel loader or articulated hauler, or any other type of vehicles, such as an automobile, motorbike, railroad vehicle, or the like.
Hybrid electric vehicle powertrains comprising a combustion engine, an electric motor and a dual clutch transmission for vehicles are known in the prior art, for example from US 2014/0171259. There is however still room for improvements in terms of drivability of the powertrain. In EP 1 826 462 A the firstly used gear disengages to become disengaged and inactive before the method opens the initially closed direct coupled gear and closes the initially open direct coupled gear. The transmission has two dog clutches. Further, the gear-changing motor unit is connected to the respective intermediate shafts through a further set of gearwheels, which gearwheels do not make a part of any one of the gears included. Other dual clutch transmissions are disclosed in US 2013/267367 A and in WO 2014/003659 A in both of which the respective transmission is combined with a planetary gear set.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
A specific problem with prior art hybrid electric vehicle powertrain designs is the relatively large mass of the rotor of the electric motor. This mass results in a relatively large moment of inertia of the rotor, which moment of inertia generally by far exceeds the total moment of inertia of the individual transmission shafts of the dual clutch transmission including any gearwheels attached thereto. The term “moment of inertia” herein refers to the rotational inertia.
The dynamic behaviour of dual clutch transmission including an electric motor attached to a transmission shaft thereof is this very different from the behaviour of a dual clutch transmission without an electric motor.
This change of dynamic behaviour is particularly noticeable during elevated acceleration levels of the transmission shafts, such as during elevated vehicle acceleration and deceleration. High vehicle acceleration typically, but not limited to, occurs when high engine torque is requested from the driver, possibly also in combination with a low loading state of the vehicle and/or a downhill road segment. High vehicle deceleration typically, but not limited to, occurs when vehicle brakes are applied and/or when engaging an uphill road segment during driving.
In a dual clutch transmission there is during driving of the vehicle generally one active gear drivingly connecting the transmission input shaft with the transmission output shaft with a first gear ratio, and one inactive gear that is prepared for becoming engaged in the future and which is arranged for drivingly connecting the transmission input shaft with the transmission output shaft with a second gear ratio. The second gear ratio may either be larger or smaller than the first gear ratio, such as to provide a change in transmission ratio. The selection between the active gear and the inactive gear is performed by selective control of the dual clutches, where one clutch is drivingly connected to the active gear and the other clutch is drivingly connected to the inactive gear.
After a gear change, i.e. after essentially simultaneous disconnection of the clutch associated with the first gear ratio and connection of the clutch associated with the second gear ratio, the first gear ratio is initially kept for a certain time period. The next required gear ratio may either be the first gear ratio again or a third gear ratio different from both the first and second gear ratio. If a transmission electronic control unit after a certain time period decides to change the currently inactive gear associated with the first gear ratio to a gear having the third gear ratio, the currently engaged inactive gear is disengaged by controlling an associated tooth clutch actuating mechanism to apply disengagement force.
The required disengagement force for disengaging the currently engaged inactive gear depends among others on the torque that is currently transmitted by the tooth clutch. One particular problem with relatively high vehicle acceleration and deceleration levels is that a relatively high torque is required when an electric motor is drivingly connected to a shaft of the currently engaged inactive gear. A rotor of the electric motor is drivingly connected to the shaft of the currently engaged inactive gear and the mass of the rotor is typically relatively high. Since the moment of inertia of the rotor depends on the mass and mass distribution of the rotor, and since the moment of inertia of any rigid body determines the torque needed for a desired angular acceleration, a relatively high torque is transmitted by the tooth clutch during driving situation having relatively high vehicle acceleration and deceleration levels.
Specifically, in situations where the electric motor is passive, i.e. not controlled to provide any output torque, the relatively large mass of the rotor of the electric motor requires the tooth clutch to transmit a relatively large torque for providing the rotor with the current angular acceleration.
The relatively high torque transmitted by the tooth clutch may require a gear disengagement force exceeding the maximal available gear disengagement force, for example due to limitations in terms of tooth clutch actuating mechanism capacity. As a result, the tooth clutch actuating mechanism may during high vehicle acceleration or deceleration levels be temporarily incapable of disengaging the inactive gear due to the high disengagement force that is required. The engagement of the next inactive gear may as a consequence be delayed, such that the next gear change also becomes delayed. Improvements in terms of drivability of the powertrain are consequently desirable.
It is desirable to provide a method for disengaging a tooth clutch of an inactive gear in a dual clutch transmission during vehicle acceleration or retardation where the previously mentioned problem is at least partly avoided.
According to an aspect of the present invention, a method is provided for shifting from a first gear to a second gear in a dual clutch transmission (10) during vehicle acceleration or retardation, the dual clutch transmission comprising:
a first gear which is engaged and active such that torque is transmitted between an engine (11) and driven wheels (4) there through, the first gear being disconnectable from the engine by a first friction clutch, the first friction clutch being closed,
a second gear to be engaged, which is disengaged and inactive such that no torque is transmitted between the engine (11) and the driven wheels (4) there through, the second gear being disconnectable from the engine by a second friction clutch, the second friction clutch being open,
an electric motor (41) drivingly connected to a shaft (21) of the one of the first gear or the second gear which is inactive,
the method comprises the steps of:                engaging the second gear to become an engaged inactive gear,        essentially simultaneously opening the first friction clutch and closing the second friction clutch such that engine torque is transmitted to the driven wheels through the second gear, thereby the first gear becomes engaged and inactive and the second gear becomes engaged and active,        controlling the electric motor (41) to provide a compensational torque for temporarily decreasing or substantially eliminating torque transferred by a tooth clutch (35) of the inactive gear,        disengaging the first gear by disengaging the tooth clutch (35) such that the first gear thereby becomes disengaged and inactive.        
By controlling the electric motor to provide a compensational torque for temporarily decreasing or substantially eliminating torque transferred by the tooth clutch of the inactive gear, the required disengagement force to be provided by the tooth clutch actuating mechanism is also decreased or substantially eliminated, thereby enabling proper disengaging the engaged inactive gear also in situations of high vehicle acceleration or deceleration. The solution thus prevents undesirable delays in gear changes, such that an improvement in terms of drivability of the powertrain is accomplished.
It is also desirable to provide a dual clutch transmission for vehicle where the previously mentioned problem is at least partly avoided.
According to an aspect of the present invention, a dual clutch transmission for a vehicle is provided comprising:
a plurality of gears,
at least a transmission shaft carrying a gearwheel;
an output shaft carrying a further gearwheel in engagement with the gearwheel of the transmission shaft,
a tooth clutch for selectively engaging and disengaging a gear composed of the gearwheels, the transmission shaft and the output shaft;
an electric motor drivingly connected to the transmission shaft; and
an electronic control unit configured for, in a vehicle acceleration or retardation mode with an engaged active gear through which torque is transmitted between an engine and driven wheels, with an engaged inactive gear to be disengaged, and with the electric motor drivingly connected to a shaft of the inactive gear,                controlling the electric motor to provide a compensational torque for temporarily decreasing or substantially eliminating torque transferred by the tooth clutch of the inactive gear,        disengaging the engaged inactive gear.        
According to some example embodiments of the disclosure, the method further comprises the step of calculating the compensational torque to be provided by the electric motor by using current acceleration or retardation level of the electric motor and at least a moment of inertia value of the electric motor. By calculating a compensational torque an appropriate torque may be immediately applied for enabling a rapid change of gear preselection.
According to some example embodiments of the disclosure, the method further comprises the step of calculating the compensational torque to be provided by the electric motor by using also current acceleration or retardation level of a transmission shaft drivingly connected to the electric motor and a moment of inertia value of said transmission shaft. Including also the moment of inertia of the transmission shaft provides a more accurate compensational torque.
According to some example embodiments of the disclosure, the method further comprises the step of calculating the compensational torque to be provided by the electric motor by using a total torque resulting from current acceleration or retardation level and moment of inertia value of each component rotationally connected to the tooth clutch of the engaged inactive gear and located upstream of said tooth clutch. Including the moment of inertia of each component provides a more accurate compensational torque.
According to some example embodiments of the disclosure, the method further comprises the step of calculating the compensational torque to be provided by the electric motor taking into account load-independent torque loss of said upstream components of said inactive gear. Including also the load-independent torque loss enables calculation of a more accurate compensational torque, in particular during cold transmission oil conditions.
According to some example embodiments of the disclosure, the method further comprises the step of determining said load-independent torque loss of said upstream components of the inactive gear takes current angular speed of the upstream components of the inactive gear into account. Including also the speed of the upstream components provides a more accurate compensational torque.
According to some example embodiments of the disclosure, the method further comprises the step of determining said load-independent torque loss of said inactive gear taking into account current transmission oil temperature. Including also transmission oil temperature provides a more accurate compensational torque.
According to some example embodiments of the disclosure, the method comprises acquiring current load-independent torque loss of said inactive gear from a data map. This approach enables a swift acquisition of data concerning current load-independent torque loss. It is also possible to update the data map if needed.
According to some example embodiments of the disclosure, the method comprises filling and/or replacing data of the data map with values by measuring load-independent torque loss of an inactive gear on an actual transmission specimen of the vehicle. This approach provides a very individual data map that takes variations within a set of dual clutch transmissions into account.
According to some example embodiments of the disclosure, the method further comprises the step of determining current acceleration or retardation level of the electric motor. This may be embodied by means of angular position sensor on the shaft of the electric motor.
According to some example embodiments of the disclosure, the method comprises controlling the electric motor to provide a gradually increasing compensational torque according to a predetermined sequence. This approach provides a non-complex and easily implementable solution for improving the disengagement of the tooth clutch using the electric motor.
According to some example embodiments of the disclosure, the gradually increasing compensational torque comprises a step-wise increasing compensational torque, or a linear or non-linear continuously increasing compensational torque. This approach enables the electric motor to provide the required output torque relatively swiftly and without knowledge of rotational speed and moment of inertia of any components of the dual clutch transmission.
According to some example embodiments of the disclosure, the step of disengaging the engaged inactive gear comprises controlling a tooth clutch actuating mechanism to apply disengagement force when an estimated and/or measured torque over the inactive gear is within a predetermined torque range, or when an estimated and/or measured torque over the inactive gear is substantially nil, or when a certain time has passed after the electric motor was controlled to provide the compensational torque, or before or simultaneous with controlling the electric motor to provide the compensational torque.
According to some example embodiments of the disclosure, the dual clutch transmission is free from a planetary transmission component in the transmission between the electric motor and combustion engine.
According to some example embodiments of the disclosure, the compensating torque is applied in the rotational direction of the electric motor during acceleration and opposite the rotational direction of the electric motor during deceleration.
According to some example embodiments of the disclosure, the method additionally comprises, after disengagement of the tooth clutch of the inactive gear, controlling the electric motor such that the relative speed between the rotating parts of a tooth clutch of a next inactive gear to be engaged is adapted for engagement. Using the electric motor for improving the synchronisation process of the next gear generally results in faster synchronisation and reduced wear on any mechanical synchronisation arrangement.
According to some example embodiments of the disclosure, a torque sensor is provided for measuring the torque of the output shaft of electric motor.
It is desirable to provide a computer program comprising program code means for performing the above-described method when said program is run on a computer, a computer readable medium carrying a computer program comprising program code means for performing the above-described method when said program product is run on a computer, an electronic control unit for controlling the electric motor of a dual clutch transmission where the electronic control unit being configured to perform the above-described method, as well as a corresponding dual clutch transmission for a vehicle, where the previously mentioned problem is at least partly avoided.
Further areas of applicability will become apparent from the description provided herein.